Some well-logging tools include a radiation detector having a scintillator coupled to a photomultiplier, which converts photons emitted from the scintillator into an electrical current for amplification. A scintillator window is positioned between the scintillator and photomultiplier. Because the scintillator and photomultiplier may be exposed to high temperatures, harsh downhole environments and excessive shock during well-logging, the scintillator and photomultiplier are contained in at least one protective housing to provide shock resistance, provide a temperature resistant seal, and accommodate differential expansion during temperature changes among the scintillator, photomultiplier, the housing and scintillator window. Also, the scintillator and photomultiplier are coupled together in a manner to maximize a diameter of the scintillator compared to the total diameter of the housing. In some cases, instead of a single housing supporting the scintillator and photomultiplier, a scintillator housing and photomultiplier housing contain the respective scintillator and photomultiplier to facilitate assembly and functional operation. The scintillator is used in well-logging tools for gamma ray measurements, natural gamma ray spectroscopy, gamma-gamma density measurement, neutron induced gamma ray spectroscopy and scintillator-based neutron detection. In well-logging, the scintillator may detect naturally occurring radioactive materials such as thorium, uranium and potassium and their radioactive decay products.